Project Summary/Abstract There is emerging evidence in the literature that diverse classes of novel ligands for asthma can acutely relax airway smooth muscle (ASM) despite a transient increase in intracellular calcium concentrations, which has classically been associated with contraction, not relaxation. Gelsolin is a calcium-activated actin severing protein that depolymerizes the actin cytoskeleton leading to ASM relaxation. Thus, activation of gelsolin by transient intracellular calcium increases may be the unifying mechanism that would account for ASM relaxation by these diverse ligands. In this proposal, we present exciting preliminary data demonstrating that mice genetically lacking gelsolin exhibit impaired ASM relaxation in vitro, ex vivo and in vivo. In addition to severing actin, intracellular gelsolin has a binding domain for phosphatidylinositol 4,5 bisphosphate (PIP2), which is the substrate for phospholipase C? synthesis of inositol triphosphate (IP3), the critical regulator of smooth muscle calcium release and contraction. We will further demonstrate that controlling intracellular gelsolin expression and activation is a therapeutic strategy for ASM cell relaxation using lentiviral-mediated overexpression of full length gelsolin and by the introduction of a short gelsolin peptide containing the binding domain for PIP2, which would selectively impair Gq-mediated increases in intracellular calcium. This proposal also demonstrate gelsolin?s role in the development of lung inflammation, which is another key pathological characteristic in asthma. We propose to demonstrate that pulmonary macrophages, in which gelsolin is abundantly expressed, can be a target for immune modulation in allergic lung inflammation. We will demonstrate that local delivery of a peptide fragment of gelsolin decreases airway smooth muscle contraction and allergic lung inflammation. A mentoring committee composed of successful scientists and physician-scientists will provide scientific expertise in each aspect of the research plan including ion channel physiology, calcium signaling, Th2 lung inflammation, lung immunology and macrophage biology. A comprehensive plan of intramural and extramural coursework and training complemented by additional collaborators with expertise in precision cut lung slices and magnetic twisting cell cytometry will expand the research training and career development. The research topic is ideal for a path to independent research in areas of airway smooth muscle pathophysiology and lung immune cell biology in allergic lung inflammation. Taken as a whole, this K08 proposal outlines a robust pathway to scientific independence and the foundation of a successful and sustained career as a physician-scientist.